For example, Japanese Patent Publication No. 4096754 discloses a positive electrode active material of a lithium-ion secondary battery.
The positive electrode active material disclosed in the literature above contains a lithium-nickel complex oxide with a layered structure. In this case, the lithium-nickel complex oxide with a layered structure is obtained by calcining a raw material mixture composed of a heat-treated product of a coprecipitate obtained by precipitating sodium hydroxide on a water-based solution containing cobalt ions, nickel ions, or aluminum ions at a predetermined composition ratio and a lithium compound. The lithium-nickel complex oxide is represented by the following general formula. General formula: LikNimCopAl(1-m-p)Or (where k, m, p, and r respectively satisfy 0.95≦k≦1.10, 0.1≦m≦0.9, 0.1≦p≦0.9, and 1.8≦r≦2.2), and Ni/Co (molar ratio) is any of 2.33, 3.0, 3.25, and 3.5. The lithium-nickel complex oxide disclosed in the literature above is a hollow particle comprising an outer shell portion on the outside and a space portion inside the outer shell portion. In addition, a ratio of a surface area of the space portion to a total surface area of the outer shell portion and the space portion in a processed profile of the hollow particle is within a range of 7% to 16%.